This invention relates to the installation of an offshore platform of the type used for oil and gas drilling and/or production operations. More particularly, this invention relates to the installation of an offshore platform having a multiplicity of jacket sections, each secured to the adjacent jacket section with a plurality of mating pins, each mating pin securing one joint.
Construction costs for offshore platforms favor onshore construction, with deep water installation providing difficult handling, transportation, launching and upending procedures for placing a prefabricated tower structure at the selected site. Therefore, the use of prefabricated, stackable jacket sections provides an alternative responsive to both onshore construction costs and offshore transportation, handling and installation costs. However, multipiece jacket installations require that the respective jacket sections or stages be mated at installation and securely interconnected. In the past, the jacket sections have been connected with long pins inserted from the surface of a fully assembled stack of jacket sections. However, this leaves the entire stack of jacket sections unsecured until length pin installation procedures are complete. Further, any misalignment or other hangup in installations anywhere within the hollow legs jeopardizes the entire pin installation.
Alternatively, it has been proposed to suspend releasable pins within the legs of the platform at each section in a position to drop onto engagement across the joints. However, this system requires complicated support and release systems within the legs and any problems with the release system would likely be remote and inaccessible to the operators.
As another alternative, shore-mounted pins have been proposed for presentation on the bottom of each upper jacket section or on the top of each lower jacket section, but this produces its own handling problems and any damage to the pins protruding from one of the jacket sections while mating with the adjoining jacket section would require costly reworking of the jacket section and significant and costly time delays.
Clearly there is a need for simpler techniques and apparatus for joining prefabricated multipiece jacket sections into offshore platforms.